The present invention relates to liquid sample dispensing in which a sampling pipette aspirates liquids from a sample or reagent container and dispenses the aspirated liquid into a reaction vessel. More particularly, the invention relates to a system for precisely delivering an amount of liquid from a sample or reagent container into a reaction tube and for reducing carry-over of liquid from one reaction tube to the next, thereby protecting the integrity of the solution within the reaction tube.
Various types of tests related to patient diagnosis and therapy can be performed by analysis of a sample of a patient""s infections, bodily fluids or abscesses. Such samples are typically placed in sample vials, extracted from the vials, combined with various reagents in special reaction vessels or tubes, incubated, and analyzed to aid in treatment of the patient. Automated clinical analyzers adapted to perform these operations typically handle liquids by aspiration and pressurized dispensing from the sample vials into a reaction vessel using a sampling probe or pipette. In general, a sampling pipette is immersed into a liquid held in a suitable container. A partial vacuum is produced in the pipette in an amount sufficient to draw the required amount of liquid up into the pipette through its nozzle, and the pipette is taken to a station holding a pre-treatment or reaction vessel. At that station, pressure is applied to the interior of the pipette in an amount sufficient to dispense the desired amount of liquid out of the nozzle. The clinical analyzer typically uses a portion or a liquot of the patient""s sample that is aspirated from the vial by a sampling pipette. The entire aspirated aliquot or a portion thereof may then be dispensed from the sampling pipette into a reaction vessel or into a sample pre-treatment vessel from which treated sample is later aspirated. Automated clinical analyzers also typically include reagent pipettes adapted to aspirate reagent from reagent containers and to dispense the entire aspirated reagent or a portion thereof into the sample pre-treatment vessel or directly into the reaction vessel.
Conventional pipettes suffer the disadvantage that liquid tends to remain on the exterior surface of the pipette when the pipette is withdrawn after aspiration. In cases of small volumes of aspirated liquid, any excess liquid carried on the exterior of the pipette may be a significant volume with respect to or could even exceed the volume of the aspirated liquid. Pipettes are designed to accurately dispense a predicted volume of liquid; however, any liquid on the exterior surface of the nozzle at the orifice might also be dispensed. Alternatively, the presence of the liquid on the exterior surface might cause the dispensed quantity of liquid to perfuse up the exterior surface, rather than to move into a target vessel. In either case, the volume of liquid received by the vessel is altered in an unpredictable fashion.
Another disadvantage is that reusable probes used to deliver liquid aliquots from successive containers such as tubes or liquid reagent vessels are a source of intra-sample carryover or contamination. Regardless of application, the sampling pipette and reagent pipette must also be thoroughly cleaned and dried between aspirations of different liquids to avoid carryover contamination.
In the prior art are various solutions to the inter-related carryover and contamination problems. To prevent cross-contamination between samples, the pipette may be provided with a removable and disposable xe2x80x9cpipette tipxe2x80x9d which is the sole portion of the probe to contact the sample liquid. However, disposable pipettes are costly and over a long period of time, become an unexpectedly high item of unwanted expense. Some analyzers include a wiping operation between each aspiration. However, wiping is an extra potential source of contamination, and also introduces additional automated mechanisms that lower the throughput rate and increase the expense of an analyzer.
In order to minimize contamination and carry-over between samples, the probe may be flushed or washed with a diluent liquid such as water. It has also been proposed to utilize a separate probe wash sleeve through which a pressurized rinse liquid is flushed (U.S. Pat. No. 4,756,201). In general, a probe wash chamber is utilized including a wash fluid input into the pipette and a fluid output or exhaust for removing the fluid once the exterior of the pipette has been cleaned. Wash chambers can leak fluid and also can channel along only one side or a portion of the pipette which can leave residue on the pipette exterior. Additionally, if a last drop of wash diluent does not drop off the pipette and is carried back to an aspiration vessel, the droplets dilute the sample or reagent, introducing unwanted sources of error.
Another technique shown, for example in U.S. Pat. No. 3,266,322, aspirates air through the probe by means of a vacuum pump or the aspirating pump used to withdraw the sample liquid from the sample container. Such aspiration, however, introduces the possibility of drawing the unwanted carry-over contaminants deeper into the tubing and apparatus which comprises the sampling system.
U.S. Pat. No. 4,347,875 discloses a xe2x80x9cself-cleaningxe2x80x9d nozzle for causing liquid remaining behind on the exterior surface of the nozzle to automatically locate itself other than at the aspirating and dispensing orifice. The nozzle comprises a liquid-confining wall extending about a longitudinal axis and terminating in a liquid-dispensing orifice, and an exterior surface having a portion adjacent to the aperture that is adapted to be immersed into a source of the liquid during aspiration. The wall attracts liquid remaining on the adjacent exterior surface after aspiration to loci spaced from the orifice a distance effective to prevent liquid remaining on the exterior surface from interfering with the dispensing of the liquid.
U.S. Pat. No. 4,871,682 discloses an air knife positioned to direct a stream or blast of air across the tip of a sample probe as it is withdrawn from a vessel containing a reagent, diluent, and patient sample solution. After the probe is flushed with diluent, the air knife drives any droplets of diluent fluid off the probe tip into the vessel and thereby prevents contamination or dilution of the sample material in the sample containers.
U.S. Pat. No. 5,506,142 discloses a wash probe in which the simultaneous introduction of pressurized air and water creates a turbulent flow including the use of a pressurized gas stream of short duration to blow the residue of the previous sample out of the probe prior to washing with additional diluent liquid. Also, a waste receptacle is provided which uses a filtered air vent and a liquid saturated material around the probe receiving opening to prevent the escape of aerosols from the receptacle.
U.S. Pat. No. 5,506,142 provides for a probe wash in which the simultaneous introduction of pressurized air and water creates a turbulent flow including the use of a pressurized gas stream of short duration to blow the residue of the previous sample out of the probe prior to washing with additional diluent liquid. Also, a waste receptacle is provided which uses a filtered air vent and a liquid saturated material around the probe receiving opening to prevent the escape of aerosols from the receptacle.
U.S. Pat. No. 5,536,471 discloses a bubble flushing syringe for aspirating and dispensing fluids through an open-ended tip. The syringe comprises a piston within a bore formed by a cylindrical wall, wherein the piston forms an annulus with the wall and closed end of the bore, and is capable of reciprocating therein. The syringe further comprises an annular seal seated in the bore and circumventing the piston to retain fluid when the piston reciprocates therethrough. An inlet for directing fluid to the annulus through the wall of the bore and an outlet for directing fluid from the annulus through the wall of the bore to the open-ended tip are positioned proximal to the annular seal and the line generally axially therebetween. A drive device is connected to the piston for reciprocating the piston within the bore. As a result, fluid from the inlet, when connected to a fluid supply, flows around the piston and through the outlet to the open-ended tip, thereby creating a cross-flow pattern in the annulus around the piston as it reciprocates in the bore to flush bubbles through the outlet.
U.S. Pat. No. 5,721,141 discloses a tube washing system including a tube spinning station having a rotatable chuck and a waste chamber surrounding the chuck for capturing and draining tube fluids expelled from a spun tube driven in rotation by the chuck. A pipette for dispensing wash water into a tube is located centrally within the chuck. There is also a tube elevating device located beneath the tube spinning station, the tube elevating device comprising a freely rotatable tube holder, and lift drive motor provided to vertically move the tube holder towards and way from the chuck. The tube used in the washing system has at least one projection provided on its open end which can interlock with a chuck groove.
U.S. Pat. No. 5,827,744 discloses method for cleaning a liquid sample probe in which the probe is positioned within a washing chamber inside a wash body and a purging liquid solution is pumped through the probe into the chamber. A cleaning liquid solution may also be pumped into the chamber around the probe. Either or both liquids are subsequently vacuumed from the chamber drawing air through an annular gap between the probe and the wash body thereby creating a cleaning air flow between the exterior probe surface and the wash body. The cleaning air flow removes all cleaning liquid solution and/or purging liquid solution as the probe is removed from the wash body.
U.S. Pat. No. 6,098,852 discloses a liquid drop dispensing container with a dispensing tip that includes a hollow stem. An interior partition wall within the stem divides the liquid passageway into an upstream chamber and a downstream chamber. The upstream chamber communicates with the interior of the container, and the downstream chamber terminates in a liquid drop outlet. A liquid passage is provided in the interior partition wall and provides flow communication between the upstream chamber and the downstream chamber. A unitary head portion extends into the downstream chamber from the partition wall and defines a rounded liquid impingement surface. Liquid passing from the upstream chamber into the downstream chamber contacts the rounded impingement surface and passes dropwise through the liquid drop outlet.
From this discussion of the art state in automated microbiological analyzers, it may be seen that while there has been considerable effort made toward the problems associated with minimizing contamination and carry-over between samples, there remains an unmet need for a simplified system to address the related problems of precisely delivering an amount of liquid from a sample or reagent container to a reaction tube and for reducing carry-over of liquid from one reaction tube to the next.
The principal object of the invention is to provide a method for using a sampling pipette that substantially reduces carryover between samples aspirated by the pipette and that is simultaneously adapted to precisely deliver an amount of liquid from a first liquid source container to a first liquid target container. An important aspect of the invention is to provide a sampling pipette in which any liquid within the target container is displaced away from the proximate vicinity of the sampling pipette by axially spinning the target container.
By spinning the target container, liquid therein is moved to inner walls and away from the central portion thereof; consequently, the sampling pipette may be lowered into the target container a sufficient distance to bring a droplet of liquid at the nozzle of the sampling pipette into contact with the bottom of the target container. Physically toughing the droplet with the bottom of the target container releases surface tension energy so that the droplet cleanly flows into the target container without contacting the sampling pipette with any liquid spun against the walls of the target container. Carryover of liquid aspirated and dispensed by the pipette may thereby be minimized between the first source container, the first target container and any subsequently accessed source and target containers.
A further aspect of the invention relates to dispensing a droplet from the sampling pipette in a first step in which a larger portion of the droplet is dispensed into a target container, optionally using the above described method for minimizing carryover of aspirated and dispensed liquids, and the smaller portion is retained within the sampling pipette. After the larger droplet is dispensed, liquid within the target container is displaced away from the proximate vicinity of the sampling pipette by axially spinning the target container, the sampling pipette is lowered into the target container to bring the smaller portion droplet of liquid into contact with the bottom of the target container so that the entire remaining smaller droplet is dispensed. Sensing to confirm the xe2x80x9ctouching-offxe2x80x9d of this smaller droplet assures that the total volume of liquid dispensed in the two steps is bounded at a maximum by the originally aspirated volume and at a minimum by the volume of liquid dispensed in the first step alone.
Briefly summarized, the invention provides a method for reducing carryover of and precisely delivering liquid from a source container to first and subsequent target containers by spinning the target containers so that any liquid within the target container is removed from the dispensing means.